This invention relates in general to systems for winding filaments into coils and in particular to an apparatus for precisely winding a coil of wire. This invention is applicable both to free standing coils and to coils which are wound upon bobbins.
Machines for winding coils of filaments, such as wires, onto bobbins are well known in the art. A typical bobbin winding machine includes a spindle upon which the bobbin is mounted for rotation. An end of a wire or other filament is secured to the bobbin, then wound thereabout as the bobbin is rotated. The wire is preferably secured adjacent to one end of the bobbin, then moved axially as the bobbin is rotated. As a result, a first layer of the wire will be wound as a plurality of adjacent windings evenly throughout the length of the bobbin before a second, overlapping layer is wound in the opposite axial direction.
To insure that the adjacent windings of the wire are closely packed together, it is desirable that the axial position of the wire feeding mechanism lag slightly behind the axial position of the point at which the wire is wound on the bobbin. Such lagging causes the windings of wire to be preloaded against one another, preventing gaps from being formed between adjacent windings. The lagging position of the wire feeding mechanism relative to the point of winding on the bobbin causes the wire to be dispensed at an angle therebetween, commonly referred as a load angle. This winding process generally results in the most efficient use of the available space provided on the bobbin.
A common problem encountered in known coil winding machines is that of precise coordination between wire feeding mechanism and the point of winding on the bobbin so as to maintain the desired lagging relationship. In theory, the optimum speed at which the wire feeding mechanism should be axially advanced can be calculated from the nominal diameter of the wire being wound, the axial length of the bobbin, and the rotational speed of the bobbin. Thus, the wire feeding mechanism can be moved so as to always maintain the wire at the desired load angle as it is wound onto the bobbin.
In practice, however, it has been found that the diameter of the wire can vary significantly from the nominal diameter, such as when different batches of wire are being wound or even between the beginning and ending of winding of a single long filament of wire. While such diameter variations are generally relatively small, they can become significant as they accumulate while a coil is being wound. This is particularly true if the nominal diameter of the wire is relatively small to begin with. Since the wire feeding mechanism is being moved axially at a speed which is based upon the nominal diameter of the wire, the accumulated error resulting from diameter variations can cause the wire feeding mechanism to be incorrectly positioned relative to the point of winding. Thus, the desired load angle is lost, and gaps may be created in the adjacent windings of the wire as it is wound in successive layers upon the bobbin. Consequently, the wire is wound in an inefficient manner on the bobbin. This is commonly referred to as coil breakup.
Several solutions have been proposed to prevent coil breakups. Some coil winding machines are provided with grooved tooling which directs the wire onto the spool at precise intervals, regardless of the diameter thereof. Unfortunately, machines of this type are expensive. Also, it is not practical to provide grooved tooling for winding wire having a very small diameter. It is also known to provide servo motors or microstepper motors for precisely positioning the wire feeding mechanism during use. However, while such stepper motors improve the accuracy of the winding process, they cannot compensate for variations in the wire diameter, as described above. Accordingly, it would be desirable to provide a coil winding mechanism which is responsive to variations in wire diameter for preventing coil breakups during the winding process.